Reactive oxygen species (ROS) are oxygen-derived small molecules including oxygen radicals such as superoxide, hydroxyl, peroxyl and alkoxyl. Through interactions with a variety of target molecules including small molecules as well as nucleic acids, proteins, lipids and carbohydrates, ROS play an important role in the regulation of diverse physiological processes. However, ROS can also irreversibly destroy or alter the function of target molecules. Excessive exposure to ROS induces oxidative stress and causes genetic mutations. ROS have been identified as a major contributor of cellular damage (Bedard & Krause (2007) Physiol. Rev. 87:245-313).
The NADPH oxidases (NOX) are transmembrane proteins that transport electrons across biological membranes to generate ROS from oxygen. Unlike other cellular elements such as mitochondria which generate ROS as a byproduct, the NOX enzymes generate ROS as their primary function. Seven members of the NOX family have been identified: NOX1 to NOX5, Duox1 and Duox2 (Bedard & Krause (2007) Physiol. Rev. 87:245-313).
NOX2, which was first identified in phagocytic cells and is often referred to as the phagocytic NOX, is also expressed in a variety of other cell types including neurons, cardiomyocytes, skeletal muscle myocytes, hepatocytes, endothelial cell and hematopoietic stem cells. Mutations in the human NOX2 gene cause chronic granulomatous disease (CGD), an immune disorder characterized by the inability of phagocytes to produce bacteria-destroying ROS. NOX2 deficient mice, which display pathological features similar to that of CGD patients, have been widely used as animal models (Sorce & Krause (2009) Antioxid. Redox. Signal. 11:2481-2504).
ROS overproduction by NOX2 has been implicated in the pathogenesis of a variety of central nervous system diseases including amyotrophic lateral sclerosis, Parkinson's disease, Alzheimer's disease, multiple sclerosis and Huntington's disease. Amyotrophic lateral sclerosis (ALS) is a progressive neurodegenerative disease that affects motor neurons. Although the cause of ALS is largely unknown, oxidative stress is believed to play a crucial role in the development of ALS. Studies have shown that NOX2 was activated in the spinal cords of ALS patients and mutant SOD1 transgenic mice, which develops motor neuron degeneration comparable to those observed in ALS patients (Wu et al. (2006) Proc. Natl. Acad. Sci. U.S.A. 103:12132-12137). Recent studies in which mutant SOD1 mice were crossed with NOX2-deficient mice showed that NOX2 deficiency delayed neurodegeneration and increased lifespan of SOD1 mice, suggesting that NOX2 may play an important role in ALS pathogenesis (Marden et al. (2007) J. Clin. Invest. 117:2913-2919; Wu et al. (2006) Proc. Natl. Acad. Sci. U.S.A. 103:12132-12137). Parkinson's disease (PD) is a neurodegenerative disease characterized by progressive degeneration of dopaminergic neurons in the substantia nigra. Oxidative stress is believed to play an important role in the degeneration of dopaminergic neurons. Studies have shown that administration of lipopolysaccharide (LPS) resulted in the release of proinflammatory factors, the activation of NOX2 and the degeneration of dopaminergic neurons (Iravani et al. (2005) Eur. J. Neurosci. 22: 317-330; Qin et al. (2004) J. Biol. Chem. 279:1415-1421). In addition, NOX2 deficient mice were shown to be significantly protected against loss of dopaminergic neurons compared to wild-type mice (Qin et al. (2004) J. Biol. Chem. 279:1415-1421). The data thus suggest that NOX2 activation plays an important role in the loss of dopaminergic neurons in PD. NOX2 has also been implicated in the development of Alzheimer's disease (AD). Studies have shown that in the brain of AD patients, markers of oxidative stress increased with severity of the disease and NOX2 is activated (de la Monte & Wands (2006) J. Alzheimers. Dis. 9:167-181; Shimohama et al. (2000) Biochem. Biophys. Res. Commun. 273:5-9). In addition, studies in which the Tg2576 mice (an animal model of AD) were crossed with NOX2 deficient mice showed that oxidative stress and cerebrovascular dysfunction do not occur in Tg2576 mice deficient in NOX2 (Park et al. (2005) J. Neurosci. 25:1769-1777). There is also evidence that NOX2 is involved in the pathogenesis of multiple sclerosis (Sorce & Krause (2009) Antioxid. Redox. Signal. 11:2481-2504) and Huntington's disease (Stack et al. (2008) Ann. N.Y. Acad. Sci. 1147:79-92).
ROS overproduction by NOX2 has also been implicated in the pathogenesis of spinal cord injury (Kim et al. (2010) Proc. Natl. Acad. Sci. U.S.A. 107:14851-14856) and traumatic brain injury (Dohi et al. (2010) J. Neuroinflamm. 7:41). In addition, ROS overproduction by NOX2 has been implicated in the pathogenesis of ocular diseases including diabetic retinopathy (Al-Shabrawey et al. (2008) IOVS 49:3231-3238; 3239-3244).
ROS overproduction by NOX2 has also been implicated in the pathogenesis of a number of cardiovascular diseases including hypertension, atherosclerosis, cardiac hypertrophy and cardiac fibrosis. Studies have shown renovascular hypertension was significantly reduced in the NOX2 deficient mice (Jung et al. (2004) Circulation 109: 1795-1801). Human atherosclerotic plaques have been found to express large amounts of NOX2 (Zhou et al. (2006) Hypertension 47:81-86). Studies have also shown that NOX2 plays an important role in angiotensin II-induced cardiac hypertrophy and cardiac fibrosis (Bendall et al. (2002) Circulation 105:293-296; Johar et al. (2006) FASEB J. 20:1546-1548). In addition, ROS production by NOX2 is also believed to be involved in the pathogenesis of stroke. Studies have shown that brain injury resulted from stroke induced in NOX2 deficient mice was significantly less than that in the wild-type mice (Walder et al. (1997) Stroke 28:2252-2258).
ROS overproduction has also been implicated in the pathogenesis of a number of reproduction diseases such as prostate cancer and preeclampsia (Lim et al. (2005) Prostate 62: 200-7; Cui et al. (2006) Placenta 27: 422-31), the pathogenesis of liver diseases such as hepatic carcinogenesis, non-alcoholic fatty liver disease, liver ischemia, liver necrosis, liver reperfusion injury (Sancho et al. (2010) J. Biol. Chem. 285:24815-24); the pathogenesis of kidney diseases such as diabetic nephropathy, chronic renal failure and acute renal failure (Fu et al. (2010) Am. J. Nephrol. 32:581-9).
One approach to the treatment of those diseases associated with ROS overproduction is to search for compounds that inhibit NOX enzymes including NOX2.